1. Field of the Invention
The present invention relates to a delivery system and method for delivering tissue supporting medical devices, and more particularly to a system and method for implanting expandable, non-removable devices at the junction of two or more bodily lumens in a living animal or human to support the organs and maintain patency.
2. Summary of the Related Art
In the past, permanent or biodegradable devices have been developed for implantation within a body passageway to maintain patency of the passageway. These devices are typically introduced percutaneously, and transported transluminally until positioned at a desired location within the body passageway. The devices are then expanded either mechanically, such as by the expansion of a mandrel or balloon positioned inside the device, or expand themselves by releasing stored energy upon actuation within the body. Once expanded within the lumen, these devices, called stents, become encapsulated within the body tissue and remain a permanent implant.
Frequently, the area to be supported by such devices is located at or near the junction of two or more lumens, called a bifurcation. In coronary angioplasty procedures, for example, it has been estimated that 15% to 20% of cases involve reinforcing the area at the junction of two arteries. Conventional stent implantation at such a junction results in at least partial blockage of the branch artery, affecting blood flow and impeding access to the branch artery for further angioplasty procedures.
Known techniques for treating bifurcations generally deliver a mesh tissue supporting device into the artery and position the device over the bifurcation. According to the known methods, a surgeon then attempts to create one or more branch lumen access holes by inserting a balloon through the sidewall of the mesh device, and then inflating the balloon to simply push the local features of the mesh aside. These techniques are inherently random in nature: the exact point of expansion in the device lattice cannot be predicted, and the device may or may not expand satisfactorily at that point. Tissue support provided by these known techniques for treating bifurcated arteries is similarly unpredictable. In addition, the effectiveness of such procedures is limited because many mesh devices are unable to accommodate such expansion at random locations in the device structure. Further, prior art tissue supporting device delivery systems are unable to accurately position specific device features over the branch artery opening.
Prior art tissue supporting devices for bifurcations generally have not attempted to orient the device radially at the branch lumen opening. Rather, these stents included a section along their axis or at one end at which several enlarged expansion cells were distributed uniformly around the stent circumference. The presumption was that after stent insertion, one or the other of these cells would be oriented closely enough with the branch lumen opening that the subsequent procedures mentioned above would clear the opening. One example of such a device is the Jostent.RTM. bifurcation stent design which has an 8 cell circumferential construction over half the stent length and either 2 or 3 rows of larger cells which can be post-dilated to allow access for placement in a bifurcated vessel. One problem with this technique is that the resulting density of stent features at the area of the bifurcation is so low that there is very little stent strength around the rest of the circumference of the main artery for tissue support. Thus, the lumen junction area, which requires the greatest tissue support, actually gets the lowest support. For the same reason, such tissue supporting devices also provide a low ratio of tissue coverage (metal-to-tissue area ratio) in the junction area. Low metal coverage and the resulting tissue prolapse are associated with higher restenosis rates.
Another method for deploying a stent in a bifurcating vessel is described in International Application WO98/19628. According to this method, a main stent having a substantially circular side opening and a flared stent having a flared end are used together to treat a bifurcating vessel in a two step process. In a first step, the main stent is positioned using an inflatable balloon catheter in the interior of the main stent and a stabilizing catheter extending through the side opening of the stent. The stabilizing catheter is used to place the side opening in the main stent at the opening to the branch vessel. The main stent is then expanded and the flared stent is inserted through the side opening into the vessel bifurcation. One drawback of this method is the difficulty in positioning the side opening of the main stent at a proper longitudinal and radial position at the vessel bifurcation. Another drawback of this system is the flared stent which is difficult to form and position, and may tend to protrude into the blood stream causing thrombosis.
In view of the drawbacks of the prior art bifurcated tissue supporting systems, it would be advantageous to have a delivery system capable of accurately locating a side port feature of a tissue supporting device at a branch lumen opening, in both the longitudinal and radial directions.
It would further be advantageous if the same delivery system could also be used to accurately install and orient a branch lumen second tissue supporting device.